Medical imaging systems nowadays are becoming ever more flexible and capable of adaptation to the respective tasks. This also includes the mechanical moving of the devices with or around the patient in order to obtain better positions for imaging or for obtaining series of images, for example. Such moving or movement is at least partly controlled by the system itself and partly by the operating personnel. Movements are thus made to specific coordinates (automatic mode) or the C-arm is repositioned, for example, by joystick deflections (manual mode). In these movements, however, there is a risk of there being an obstacle or even a patient in the path of the movement. There is thus the acute danger of bruising and other injuries.
For such collision problems there are already approach protection mechanisms provided by pressure sensor systems. However, triggering of any sensor system indicates that a collision with the obstacle has already happened. In order to prevent this, different proximity systems such as ultrasound sensors, infrared sensors or capacitive measurement systems are used. A disadvantage here however is that these systems may only detect an approach, but not a collision in the required safety class (comparable to SIL2 or to the first-error security additionally demanded in medical technology, according to which any error must immediately be recognized and reported). Another disadvantage is that liquids on the surface of the device, from an operating theater, for example, adversely effect capacitive sensors lying under the casing and make an exact proximity measurement impossible, since the dielectricity constant of the medium (e.g., of the measurement range) is so high that an intrusion of a part of the body into the measurement range will no longer be perceived at all.
Dedicated systems have thus previously been used for the proximity sensor systems and separate systems for the collision recognition. With collision recognition, an emergency stop is triggered that brings the system to a halt immediately and remains active until the cause of the triggering has been rectified and the system no longer recognizes a collision. With the proximity sensor systems, for example, an emergency stop may likewise be triggered as from a specific threshold value in the evaluation. However, provided that a distance value to an object is identified, just the speed of approach may be reduced (e.g., linearly or exponentially). The advantage of proximity sensor systems is that any possible halt of the system may already be initiated shortly before the real collision.
The advantage of collision recognition is that the evaluation may be done via a mechanical signal that may not be influenced by wetting by liquids or the like, that enables this collision recognition to also be configured for safety. For example, with a supervision measure a signal abort occurs when the sensor is touched and activated by the object. With a non-contact sensor this function supervision may not be carried out until the last relevant point.